DBA/2 mice are resistant to induction of disease by Friend MuLV, a process which appears to require the formation of recombinant MCF viruses. This resistance appears to be due to the presence of an endogenous MCF-like glycoprotein on the surface of DBA/2 cells, which blocks MCF receptors on these cells. A gag-pol-env+ replication-defective MuLV was characterized and was used in experiments analyzing the resistance of DBA/2 cells to MCF. Treatment of DNA/2 cells, as well as cells producing MuLVs, with inhibitors of glycosylation reverses viral interference.